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Thursday, September 24, 2009

The outcome of an extensive genetic research suggests that the population of India was founded on two ancient groups that are as genetically distinct from each other as they are from other Asians, according to the largest DNA survey of Indian heritage to date. Nowadays, however, most Indians are a genetic hotchpotch of both ancestries, despite the populous nation's highly stratified social structure.

A team led by David Reich of the Broad Institute in Cambridge, Massachusetts and Lalji Singh of the Centre for Cellular and Molecular Biology in Hyderabad, India probed more than 560,000 DNA-letter differences, called single nucleotide polymorphisms (SNP) across the genomes of 132 Indian individuals from 25 diverse ethnic and tribal groups dotted all over India.

The researchers showed that most Indian populations are genetic admixtures of two ancient, genetically divergent groups, which each contributed around 40-60% of the DNA to most present-day populations. One ancestral lineage — which is genetically similar to Middle Eastern, Central Asian and European populations — was higher in upper-caste individuals and speakers of Indo-European languages such as Hindi, the researchers found. The other lineage was not close to any group outside the subcontinent and was most common in people indigenous to the Andaman Islands a remote archipelago in the Bay of Bengal.

Indian populations, although currently huge in number, were also founded by relatively small bands of individuals, the study suggests. Overall, the picture that emerges is of ancient genetic mixture, followed by fragmentation into small, isolated ethnic groups, which were then kept distinct for thousands of years because of limited intermarriage — a practice also known as endogamy.